Keyword searching of large document collections has become a routine activity for many types of businesses and consumers. The interface provided to a user for performing a keyword search can be relatively simple, and lists of responsive documents are often provided in a few seconds or less. However, extensive resources are required to provide this functionality. This can include large groupings of computers that can maintain information about the documents in a large document collection, and that can further allow for rapid identification of documents that are responsive to search queries.